Traffic cycle length selector



July 31, 1962 Filed NOV. 5, 1958 G. D; HENDRICKS TRAFFIC CYCLE LENGTHSELECTOR 5 Sheets-Sheet l 'STl sra maouno OUTBOUND TRAFFIC TRAFFICDENSITY DENSITY COMPUTER COMPUTER 1c oc 00 I AMPLIFIER VOLTAGE CYCLELENGTH DETECTOR GENERATOR AND v0 SELECTOR cs CGA LDI 0GB 1c LD2 CGCAMPLIFIER VOLTAGE o0 DETECTOR LD3 cs0 LD4 CGE 0 L05 CGF INVENTOR. LEVELCYCLE I K DETECTORS GENERATORS G'DONALD HENDR C s iiwA ATTO RNEY July31, 1962 G. D. HENDRICKS 3,047,833

TRAFFIC CYCLE LENGTH SELECTOR Filed Nov. 5, 1958 5 Sheets-Sheet 2 LG EliJ e m9 D E ll OUTBOUND TRAFFIC cc\ DENSITY COMPUTER 00 VOLT A 65 CYCLELENGTH DETECTOR GENERATOR A INBOUND v D AND SELECTOR Tlgfillgqc cs 0 I Y00 COMPUT IC FL, c LC 7 /IST EJP1 i122 s -il 2 T10" I I T ANTENNA Ic-|GEN kI OR fl SENS'T'VE TRIZYJS- ELECTOR TSM TR oc-| cs I TONE ANTENNAGENERATOR T a Y CYCLE TIMING FM IE I TONE SENSITIVE MOTOR RECEIVERAMPLIFIER DEMODULATOR XR TSD 7 TT AMPLIFIER INVENTOR.

FIG. 5

G. DONALD HE NDRIGK 8 BY ATTORNEY G. D. HENDRICKS 3,047,838 TRAFFICCYCLE LENGTH SELECTOR Jul 31, 1962 Filed Nov. 3, 1958 5 Sheets-Sheet 3REED OSCILLATORS INVENTO R G-DONALD HENDRICKS ATTORNEY July 31, 1962 G.D. HENDRICKS TRAFFIC CYCLE LENGTH SELECTOR 5 Sheets-Sheet 4 Filed NOV.3, 1958 s T K o m R Y H MW%E ME N u VH R MD 0 L/ A A T m M a A V D "F G.T Y5 B B R m R as E E F E l LE HA M AA u B PRE AMPLIFIERS 5Sheets-Sheet 5 .2 .2 w 2 2 Nw ow m a. mm J J 3 1E M M vwvwmv wvwwwwww vm I r M C W .wo .w? m? .mi. m mg m wm3 m5 m2 mmm M a A 6-7 N mm m 0$$$999 6. W m T July 31, 1962 G. D. HENDRICKS TRAFFIC cycuz: LENGTHSELECTOR Filed Nov. 5, 1958 aposite direction.

This invention relates to improvements on trailic supervised apparatuswhich automatically relates the duration of a traffic signal cycle tothe volume of trafiic in the direction of heavier trafiic along athoroughfare.

The invention relates also to improvements in tratlic sampling andcontrol on a system of city streets forming a grid. One or more typicalstreets is selected for sampling, the streets chosen beingrepresentative of those within the entire grid.

It has long been realized that different volumes of trafiic can best behandled with trafiic signals set for different cycle lengths. Lighttramc flows most expeditiously through a series of intersectionssignaled with a short cycle that does not appreciably delay a vehicleeither on the thoroughfare or on the cross street. As trailic volumeincreases, progressively longer trafiic cycles are required to passlarger numbers of vehicles with fewer stops and starts.

Until recent years, changes in tratfic cycle length have been programmedfrom a central station according to a predetermined pattern establishedfrom traffic counts and other estimates. However, traflic does notalways follow the predetermined pattern and may increase or decrease atvarious times for various reasons.

The invention relates to apparatus which permits frequent adjustment ofthe traffic cycle length based on a 100 percent trafiic sample thuspermitting high accuracy. The sample is taken at the entry points to thegrid or thoroughfare permitting anticipation of change in tratficconditions within the grid. The apparatus in the local controllers alsopermits instantaneous lengthening or shortening of the cycle during anyportion thereof without altering the split or offset. A change in cyclelength does not disrupt the split of the cycle between the thoroughfareand the cross street, nor does it interrupt the progressive offset. Theapparatus thus effects a smooth transition from one cycle length toanother.

Another feature of the invention is its ability to determine cyclelength from the volume of trafiic in the heavier direction along one ormore throughways. Known systems base the cycle length on the totalvolume of trafiic in both directions on one street. It is evident thattratfic conditions are entirely different when, for example, 400vehicles travel in each direction than when 700 vehicles travel in onedirection and 100 vehicles travel in the op- The apparatus disclosedherein determines the volume of traffic in each direction, selects thehigher, and determines the cycle length therefrom. Thus, a morerealistic cycle length is effected.

One portion of the apparatus is embodied in a novel electronic levelselector shown in its preferred form as having six levels. More or fewerlevels may be employed without departing from the spirit of theinvention. The level selector operates in conjunction with a number ofvibrating reed type cycle generators making only one generator effectiveat a time to supply a particular signal frequency over aninterconnecting channel to the drive motor in each local trafliccontroller. An amplifier is employed with the cycle selector to boostthe power output of the device so that it can drive a number of localcontroller motors. A novel amplifier is employed in each localcontroller to amplify the incoming signal and to increase the potentialapplied to the motor in proportion to the frequency so that the motorcan supply substantially the same torque at all speeds. Such anamplifier is disclosed in United States patent application 830,03 8,filed July 28, 1959, entitled Constant Current Trafiic ControlAmplifier, now abandoned.

Another feature of the portion of the invention within the localcontroller is its ability to change the complete cycle length ratherthan only portions thereof. Known cycle changers alter the cycle duringthe variable portions and switch to constant timing power for the amberintervals, The present invention changes the entire cycle making thesame percentage change to each variable portion. A second constanttiming device times each constant portion of the cycle. This makes theunit easy to set upand easy to change. The cycle speeds are directreading; there is no need to add two variable timers and two constanttimers to determine total cycle length.

Within one complete traflic cycle there may be any number of variableand constant timing intervals. Additional dial keys are simply insertedin the two dials at each local controller. The device is also easy toconvert from two-street to three-street operation, simply by insertingdial keys and breaking out signal-controlling cams.

Another feature of the invention is its ability to control cycle lengthat a number of local trafific controllers through the use of a singleradio channel. The output of a tone generator is modulated by varioustones from any one of the vibrating-reed type cycle generators andapplied to a radio transmitter. A receiver at each local controllerincludes an amplifier, a demodulator, a second amplifier, and asynchronous motor which drives the signal changing device. Othersignaling impulses including resynchronizing pulses, offset selectingpulses, and split selecting pulses may be transmitted simultaneouslywithout affecting the cycle speed. The radio link is disclosed morefully in United States patent application 830,096, filed July 28, 1959,entitled Remote Control of Traffic Cycle Length.

The present invention is an improvement over any cycle determiningdevice known in the art. 'It attacks the problem directly. It employstwo tratfic density computers each of which develops an output potentialproportional to the volume of tralfic in each direction along one ormore thoroughfares, a voltage detector to determine the higher density,a plurality of trafiic volume level selectors, and a plurality of cyclegenerators any one of which may be chosen to energize a conductorconnected to a motor in each local controller to drive it at one of aplurality of speeds. In another embodiment of the invention a tonesensitive modulator and a radio transmitter may be used with a radioreceiver and tone sensitive demodulator in each local controller. In athird embodiment of the invention an electro-mechanical gear changer maybe employed in each local controller to change its cycle speed, thegears being shifted remotely under control of the volume levelselectors. Such a gear changer is disclosed in United States patentapplication 727,741, filed April 10, 1958, entitled Tratfic CycleSelector Apparatus.

Objects The principal object of the invention is to provide an improvedelectronic traffic control device able to determine trafiic cycle lengthfor an area including intersecting street-s from the density of trafficin the heavier direction on one or more thoroughfares.

It is another object of the invention to provide electronic apparatusfor determining thev density of traffic in both directions on a street,discerning the higher, and using the higher density to select a trafliccycle length.

It is another object of the invention to provide apparatus at a centralstation for generating a plurality of discrete frequencies and formaking any one of six frequencies corresponding to six levels of trafficdensity effective to control the length of a traffic cycle.

It is another object of the invention to provide apparatus at aplurality of local traffic signal controllers for receiving andamplifying any one of a number of frequencies and for operating asynchronous motor therefrom to control the duration of a traflic cycle.

It is another object of the invention to provide an amplifier at eachlocal controller whose output potential is proportional to its inputfrequency.

It is another object of the invention to provide a trafiic levelselector which energizes one of a group of signal generators whenenergized by a potential gradually variable over a wide range.

It is another object of the invention to provide a generator of discretefrequencies only one of which is amplified at a time depending upon thehigher density of traffic on a thoroughfare.

It is another object of the invention to select according to highertraffic density and amplify the output of only one of a group ofcontinuously opera-ting signal generators and to transmit the amplifiedsignal to a group of local controllers to precisely control their speed.

It is another object of the invention to provide a tone generatormodulated by various tones representive of various cycle lengths, aradio transmitter, and a plurality of local controllers each including aradio receiver, a tone sensitive demodulator, an amplifier, and a cycletimer.

It is another object of the invention to provide a level detector todetermine the level of traffic in the heavier direction, a group ofinterconnecting channels, and a group of local controllers each having aconstant speed motor, and a cycle timing unit driven by the motorthrough a gear train shif-table over the interconnecting channel.

Figures The invention will be described with reference to the followingdrawings, of which,

FIGURE 1 is a plan view of a six lane highway having traffic actuateddetectors in each lane, inbound and outbound traffic density computers,a voltage detector, a cycle length generator and selector, an amplifier,and a conductor to the local controllers.

FIGURE 2. is a plan view of two one way streets having detectors in allthe lanes, two traffic density computers, a voltage detector, a cyclelength generator and selector, an amplifier, and a single channel to thelocal controllers.

FIGURE 3 is a block diagram of a cycle length selector including avoltage detector, level detectors, cycle generators, and amplifier.

FIGURES 4 and 4A are a wiring diagram of the cycle length generator andselector having five level detectors, six oscillators, sixpreamplifiers, and an amplifier.

FIGURE 5 is a block diagram of a system for transmitting the variablefrequency signal using radio.

FIGURE 6 is an isometric view of the cycle timing apparatus in a localcontroller. The wiring associated with the unit is also shown.

Grid System Controlled by T rafiic on T wo-Way Streets A typicalapplication of the invention is shown in FIG URE 1. A six lane street STis shown for purposes of illustration; the street may have more or fewerlanes, however. The street has a number of intersecting streets STl,ST2, only two of which are shown. Local intersection trafiic controllersLC control the traffic signals S along the street ST according to anumber of plans whose selection forms the subject of this invention.

A traffic density computer is employed for each direction of traffic.The inbound and outbound traffic density computers are labeled IC andOC. Traffic actuable detectors are installed in each lane of the streetST. Detectors D1, D2, D3 in the inbound lanes 1, 2, 3 feed trafficinformation to the inbound computer IC. Detectors D4, D5, D6 in theoutbound lanes 4, 5, 6 feed traffic information to the outbound computerOC. The most accurate sampling is done with detectors in all traveledlanes, but detectors may be omitted from some of the lesser traveled andparking lanes with only a slight reduction in accuracy. Any of the knowntypes of detectors may be used including pressure, electromagnetic,electrostatic, radar, photo electric, or infrared. Detectors of thepressure type will be used in the illustration because they are thesimplest to apply, requiring no auxiliary apparatus.

Each traffic density computer as presently constructed is adaptedtoreceive the output of as many as five traffic actuated detectors. Acomplete disclosure of a traffic density computer usable with thisinvention may be found in United States patent application 738,327,entitled Trafiic Lane Control," filed May 28, 1958. The function of acomputer is to provide a direct current output potential proportional totratfic density in one direction. The computers receive signals from thedetectors, reduce the signals to a pulse of short duration, eliminatemost of the noise accompanying the signals, reduce the pulses by afactor of two, give the remaining pulses a definite duration, integratethe pulse count over a short interval, integrate the count over a longinterval, and develop a potential proportional to the integrated count.The output of each computer is available for a number of purposes andmay also be read on a meter entitled Vehicles per Hour.

The output of each traffic density computer IC, 0C is fed to asimplified voltage detector VD consisting of two silicone diodes. Bothvoltages, indicative of traffic density in each direction, are passed bythe diodes with the higher voltage being effective in the cycle lengthselector SC. The lower voltage has no further effect. The output ofeither computer IC or 00 does not affect the other because of the highback-impedance of the diodes.

The output of the higher traffic density computer IC or 0C is thusapplied to the cycle length generator and selector CS. This consists ofa plurality of level detectors, a corresponding group of low frequencyoscillators and preamplifiers, and an amplifier. If the incomingpotential is not sufiiciently high to overcome the lowest leveldetector, a first cycle plan remains in effect. As trafiic densityincreases and the potential rises it overcomes successively higher leveldetectors. The highest level detector to be energized makes effectiveits corresponding oscillator-amplifier circuit and makes ineffective alllower oscillator-amplifier circuits. The output of the highest effectiveoscillator-amplifier circuit is amplified it amplifier A and transmittedover a single channel CC to all local controllers LC. The localcontrollers LC are of the type disclosed in United States patentapplication 642,469, entitled Multiple Program Traflic Control Systems,filed February 26, 1957. Apparatus described in the present applicationadapts the local controllers disclosed in application 642,469 to receivethe variable frequency, amplify it, "boost its potential in proportionto the frequency, and energize a synchronous timing motor which drivesthe cycle dial at a speed exactly proportional to frequency. The speedof the cycle dial determines the duration of the various traffic signalintervals comprising the signal cycle. Power to operate the localcontrollers LC and to illuminate the signals S is taken from lines L1,L2.

Thus the duration of the traffic signal cycle within an entire area of acity is made to vary in incremental steps substantially proportional tothe density of traflic in the heavier direction on a typicalthoroughfare.

Trafiic System Controlled by Trafiic on One-Way Streets Anotherapplication of the invention is shown in FIG- URE 2. The invention maybe used on city streets one or more blocks apart that are designated forone-way travel, or on a divided highway having intersecting streets. Thestreet carrying inbound tralfic is labeled IST and has detectors Dll-DISmounted in its five lanes. The street carrying outbound traffic islabeled 0ST and has detectors D16-D20 in its lane Any of the ,knowntypes of trafiic detectors may be used; pressure sensitive detectors areshown for simplicity. In the interest of economy, one or more of thelesser traveled lanes may not be detected. This reduces the accuracy ofthe count somewhat, depending on the relative weight of the undetectedlanes.

The output of each of the five detectors Dll-DIS in the inbound streetIST is fed to individual input terminals on the inbound traflic densitycomputer IC. The output of each of the five detectors D16-D20 in theoutbound street 0ST is fed to individual input terminals on the outboundtrafiic density computer 0C. In practice, each computer is built toinclude five individual input circuits. Individual circuits are requiredso that almost simultaneous signals may be differentiated and not lost.

Each pressure sensitive trafiic detector closes a circuit when actuatedby traffic, the circuit usually being closed to ground potential. Twosignals are initiated, one for each set of wheels passing over thedetector. The signal originated by closure of the detector contactplates is characterized by contact chatter, bounce, and noise. It is thefunction of the input stages of each computer IC, CC to convert thenoisy signal to a chatter-free pulse, one for each axle. The inputstages amplify and clarify the signal, give it a very short duration,and reduce two pulses to one. The pulse is reduced to one of shortduration so that pulses arriving almost simultaneously will not beimposed on top of each other and lost. Two pulses are reduced to one sothat the count of vehicles, not axles, will be registered The shortpulses are next given a uniform duration and amplitude, and are thenintegrated over a short interval. A potential is developed whichrepresents the running average of vehicles arriving over a continuous 20second interval. This count is next integrated over a variable, runninginterval which may include counts up to 9 minutes old. A potential isdeveloped to represent the running average of trafiic density in onedirection integrated over the running 9 minute interval. The computersare described in detail in application 73 8,327, noted above.

Potentials representative of the density of tratfic in each directionare fed from inbound and outbound computers IC, OC to a voltage detectorcircuit VD. The circuit consists simply of two diodes each of which isarranged to pass the potential impressed on it. The higher potential isapplied to the cycle length generator and selector CS. The lowerpotential has no effect. One computer is kept from backfeeding to theother by the high back-impedance of the diodes.

In the cycle selector CS the input potential is fed to a group ofsuccessively higher biased level detectors. When the input potential isso low that it does not energize any level detector, a first oscillatorand pre-amplifier is free to energize an amplifier A. The amplifiedsignal frequency is transmitted over an interconnecting channel CC toeach local trafiic signal controller LC. At the local controller LC thesignal frequency may again be amplified, increased in potential andutilized to drive a synchronous motor. The motor in turn drives a cycledial which times the duration of the traffic cycle.

When traffic density increases and the input potential to the leveldetectors increases, successively higher level detectors are energizedwhich in turn make successively lower frequency oscillators eflective.Only one oscillator is effective at a time although all oscillatorsoperate simultaneously and continuously. Only the oscillator andpre-amplifier corresponding to the highest energized level detector isswitched to be effective at any time. All pro-amplifiers are connectedto the amplifier A which amplifies the signal from the effectiveoscillator and preamplifier. The amplified signal is transmitted to thelocal controllers LC where it determines the speed of the synchronouscycle dial motor and thus the duration of the traffic signal cycle.

The cycle of signal change in an entire section of a city is thus madeto conform to trafiic density on one typical thoroughfare, whether thethoroughfare consists of one-way or two-way streets. In the one-waystreet system it is important to relate the duration of the cycle to theheavier direction of trafiic and to interconnect all controllers alongboth one-way streets to permit the coordination of cross street traflic.

There may be instances where trafiic cycle length may be determinedsimply by flow of traflic in one directionas on a one-way street widelyseparated from. its companion one-way street. If coordination of crossstreet tralfic may be disregarded, each direction of traffic may haveits own independent cycle length. The apparatus required for each streetmay be reduced to one traffic density' computer, a cycle lengthgenerator and selector CS, an amplifier A, an interconnecting cable CC,and a group of local controllers LC. Since this application would findonly limited use, and since the various components are identical withthose described, the single street systerm will not be furtherdescribed.

Cycle Selector Having described the operation of the complete system,the cycle length generator and selector will now be described.

FIGURE 2 shows that the output of the inbound or outbound tratficdensity computer, IC or OC whichever is higher, is applied to the cyclelength selector CS from the voltage detector VD. The higher potential isused as a measure of traific density on the thoroughfare and the cyclelength is determined therefrom.

Referring now to FIGURE 3, th voltage detector VD consists of twoselenium diodes which pass the positive direct-current potential fromthe traflic volume computers IC, OC. The output of the circuit is apotential representative of traffic in the heavier direction and isapplied to all of the level detectors LDl-LDS simultaneously. Successivelevel detectors are biased with successively higher biases producing aladder effect. The bias voltage for each level is adjustable so thatdifferent steps in traffic density will be required to trigger thevarious level detectors. The steps may be those commonly used in trafiiccontrol such as 100, 200, 300, 400, 500, 600 vehicles per hour per lane,for example. The steps may also be calibrated in percent of trafficvolume at which the change from one cycle length to the next cyclelength is to be made.

When the density of trafiic is very low, as during the hours frommidnight to early morning, none of the level detectors LDl-LDS isenergized and thus cycle generator CGA is permitted to operate. Cycle Ais thus in effect. Cycle A may be the shortest length cycle or maypermit all local traflic actuated controllers to dwell with theright-of-way signal illuminated to the main street. If trafiic actuatedcontrollers are used they are permitted to answer calls from trafficarriving on the cross street.

Calls may be answered as they occur, or they may be delayed until abackground cycle impulse indicates to successive controllers that thetime reserved for main street traflic has transpired and that crossstreet calls may be answered. If pretimed controllers are used, thesignals may be set to provide a flashing right-of-way indication to mainstreet traflic and a flashing stop indication to cross street traflic.This permits cross street traffic to proceed with caution after a fullstop, yielding the rightof-way to main street trafiic.

As trafiic density increases during the morning hours the potential fromone of the traflic density computers IC, OC may be sufiicient toovercome the bias voltage on the first level detector LD1. When thisoccurs the first level detector LDI energizes a relay which switchesplate potential from an amplifier associated with cycle generator CGAand applies plate potential to an amplifier associated with cyclegenerator CGB. Cycle B is thus in effect. Cycle B may be a slightlylonger cycle or may be a plan which permits the local traffic actuatedcontrollers to answer calls only at certain intermittent times. Thus, acycle length is established.

As traflic density builds up further it may require additional change incycle length. As the potential from either of the traific densitycomputers IC or OC increases, it will be sufficient to overcomesuccessively higher biases and cause one of the higher level detectorsLD2-LD5 to conduct. As any one level detector LD2LD5 becomes effectiveit energizes its corresponding cycle generator preamplifier CGC-CGF,respectively, and deenergizes the preamplifier associated with the nextlower cycle generator. Only one cycle generator is effective at anytime. The cycle generators and their controlling reed vibrators are alloscillating all of the time to reduce the start-up interval and to makethe full generator frequency available instantly as required. Theirpreamplifiers are switched on or off to make the desired cycle generatoreffective.

Amplifier A receives the preamplified signal from the effectivepreamplifier associated with cycle generators CGA-CGF. Here the selectedfrequency is amplified before it is sent out on an interconnectingchannel CC to all the local controllers LC. In each local controller LCthe signal is again amplified and increased in potential before it isapplied to the synchronous motor which drives the cycle timing dial. Theportion of the apparatus located in the local controller is shown inFIGURE 6 and is described in greater detail in a later section.

Cycle F, the cycle plan put into effect when traffic density isgreatest, may constitute the longest cycle length employed or may be aplan for simultaneous operation of a group of controllers. Simultaneousoperation may include a number of controllers operating in unison, ormay include a multiple alternate offset plan. The plan chosen to be putinto effect would be the plan found to handle heavy trafiic mostefficiently for the thoroughfares involved. The plan found to be mosteflicient in one city may not be satisfactory in another. Therefore, theplans are made flexible so that the largest number of installations canbe accommodated.

The device used to adapt the cycle determining frequency to one suitablefor transmission over a radio channel is shown in block diagram inFIGURE and is disclosed in detail in United States patent application830,- 096, named above. The device used topick up and amplify the signalat each local controller is disclosed in United States patentapplication 830,038, also named above, and now abandoned.

Cycle Generator and Cycle Selectoir A complete wiring diagram of thecycle generator including reed oscillators, oscillator control circuits,preamplifiers, amplifier, level detectors and plate relays is shown inFIGURES 4 and 4A. FIGURE 4A may be placed to the right of FIGURE 4 inorder to view the circuit diagram in its entirety. Six reed oscillatorsare shown at the left of FIGURE 4. Six oscillator control circuits areshown at the right. Six grid leads continue to the right border and arerepeated at the left of FIGURE 4A. FIGURE 4A shows three doublepreamplifier tubes. Along the right border are shown five potentialdividers, and five level detector tubes. Above the level detectors is afinal amplifier tube and the output terminal OT. Between thepreamplifiers and the level detectors are the plate circuit relays. Eachlevel detector controls a plate circuit relay which applies platevoltage to a single preamplifier which in turn makes one oscillatorcontrol circuit effective. greater detail.

A plurality of resonant reed oscillator controls 11A- The circuit willnow be described in v 11F are employed to control the frequency ofoscillation of an equal number of oscillator control circuits. Theresonant reed oscillator control is an electromechanical device of thetype described more fully in James G. Biddle Company Bulletin 34-10,dated March 1957. The drive coil 13 is connected in the cathode circuitof triode V1B. When plate potential is applied to terminals marked 3+,tube V1B draws current through drive coil 13 located in its cathodecircuit. Drive coil 13 creates a magnetic flux in the reed 14 whichmomentarily polarizes it allowing the tip of drive reed 14 tomomentarily become a magnetic pole. The flux in the coil and thatinduced in the reed tip interact causing the reed to move toward theopposite pole of the coil. This motion of drive reed 14 is transmittedthrough the rigid metal bar 15 to reed 16. Control reed 16 is mountedinside of control coil 17; as the tip of control reed 16 moves insidecoil 17 its fiux changes and induces a potential in control coil 17.This potential is applied to the grid of tube VIA causing a change inplate current through resistor R1. Increased current through resistor R1causes a reduction in potential on the left side of capacitor C1.Now-surplus electrons on the right side of capacitor C1 flow to groundthrough resistor R2 increasing the negative bias applied to the grid oftube V1B through resistor R3, thus decreasing its current flow.

Decreased current fiow through the plate circuit of tube V1B results inreduced current through drive coil 13. 1f the values of capacitors C1,C2 and resistors R1R5 are properly chosen, an oscillatory condition willresult causing increased motion of drive reed 14. The amplitude oftravel of drive reed 14 increases with each successive current pulseuntil vibration at the reeds natural frequency is maintained.Oscillation of control reed 16 will control and sustain the oscillationof the tube circuits VIA, V1B through the potential induced in controlcoil 17. The circuit will continue to oscillate producing a signal ofnearly sinusoidal waveform and at the exact frequency of reeds 14 and16.

Resistor R5 is placed in the cathode circuit of tube V1A to reduce thecathode potential and aid cut-off. Resistor R4 limits the plate currentin tube VlB. Capacitor C2 acts to smooth out the current flow throughresistor R4.

The output of the controlled oscillation circuit is taken off belowplate circuit resistor R1 through coupling capacitor C3. PotentiometerR6 is connected between capacitor C3 and ground. Its tap applies thecontrolled frequency sinusoidal signal to the grid of preamplifier tubeV7A, FIGURE 4A, through grid resistor R7.

Any number of reed oscillator controlled circuits may be employed in thecycle generator, one being required for each cycle length desired. Sixoscillator circuits asscciated with tubes V1A, VIB to V6A, V6B areshown, each having different values of resistance and capacitance, andeach having reed oscillators 11A-11F tuned for different frequencies.

Plate voltage 13+ and filament voltage is applied to all the oscillatorcircuits continuously. Thus, all oscillator circuits are functioningsimultaneously. Plate voltage is applied to only one preamplifier V7A,V7B to V9A, V93, FIGURE 14A, at a time. Which tube receives platevoltage depends on the position of relay switches 21-25, FIGURE 4A,which in turn depends on the condition of level detector tubes VII-V15.The condition of level detector tubes V11-V15 is determined by the levelof the input potential from the higher traffic density computer 1C orOC.

Preamplifier tube V7A, FIGURE 4A, has plate volt age applied to itthrough resistor R3 When the input potential to the grids of the leveldetector tubes V11-V15 is low and none of the detector tubes isconducting. With none of the relays 21-25 energized, the plate voltagecircuit is complete from terminal B-]-, through relay contacts 25A, 25B,through relay contacts 24A, 24B; 23A, 23B; 22A, 22B; 21A, 21B, throughresistor R8 to the plate of tube V7A. Tube V7A conducts if gridpotential is applied from oscillator tube V1A. Resistor R9 in thecathode circuit of tube V7A aids cutoff. The circuit configurationamplifies the output of the oscillator maintaining the sinusoidalwaveshape of the signal.

The output of the circuit is applied to the grids of final amplifiertube halves VltlA and VltlB through coupling capacitor C4. Both halvesof tube V10 are connected in parallel to increase the capacity of thetube.

Resistor R10 is a grid leak resistor associated with both grids of tubeV10. Resistor R11 is a cathode follower resistor. The output potentialof the cathode follower circuit is taken off through coupling capacitorC and applied to output terminal OT. Plate voltage B-lis applied to bothplates of tube V continuously while the master controller isfunctioning. The output of the device is supplied to all localcontrollers over the single channel CC, FIGURES l and 2.

The operation of the level detectors will now be described. TubesV11-V15 are of the thyratron type. They form a level detector. Thepotential representative of trafiic density is applied to all the grids,but through successively higher impedances and against successively morenegative bias voltages. A plate circuit relay controls the platepotential to the next lower level detector tube and to the next lowerpreamplifier tube. (The lower level detectors are shown near the top ofFIGURE 4A and the higher level detectors are shown near the bottom ofthe figure.) The plate circuit relay also controls power to a neonindicator A-F which shows which level is effective.

One level detector will be described in detail; the others are identicalexcept for impedance values. A negative bias potential 105 v. is appliedover line 41 to an adjustable voltage reducing network consisting of avariable resistor R12, a potentiometer R13, and a fixed resistor R14connected to ground. A tap on potentiometer R13 applies an adjustablenegative bias potential to the control grid of tube V11 through gridresistor R15.

The potential representative of traffic volume in the heavier directionarrives from voltage detector VD and is applied to the level detectorgrids through conductor 42 and grid resistor R16. The difference inpositive and negative potentials is effective to control tube V11.Capacitor C6 is connected between the grid and cathode for tubeprotection purposes. The screen grid is connected to the cathode and toground.

The plate of tube V11 is connected to a source L2 of 120 volts A.C.through the coil of plate circuit relay 21 and through normally closedcontacts on the plate circuit relays 2225 of all the higher leveldetectors. Plate circuit relay 21 connects the plate of the lowest levelpreamplifier tube V7A to positive plate potential B+ through contacts21A, 2113 when deenergized. When energized, relay 21 connects the platecircuit of the next level preamplifier tube V7B to B+ through contacts21A, 21C. Capacitor C7 is connected in parallel with the coil of relay21 to maintain the current therethrough during the negative half cycleof the 60 cycle supply L2.

Resistor R17 is switched into the grid bias circuit in parallel withresistor R14 by relay contacts 21G when relay 21 is energized. Thispermits the circuit to respond to reduction in density-representativepotential and fall back to level A when density decreases.

Pilot lamp A is illuminated when the lowest level preamplifier isoperating. It is energized from source L2 through contacts 25D, 25E;24D, 24E; 23D, 23E; 22D, 22E; and 21D, 21E. Other pilot lamps B, C, D,E, F are provided to indicate higher levels and are energized throughcontacts ZIP-25F, respectively.

To trace a level change, assume that tube V11 is conducting, relay 21 isenergized and preamplifier V7B is effective. Its signal output is takenoff through coupling capacitor C4 and applied to the grids of tube V10.A sinusoidal oscillation at the frequency established by 10 reedoscillator 11B and tubes V2A, V2B, FIGURE 4, appears at output terminalOT, FIGURE 4A.

Assume now that traffic density increases to a value that permits leveldetector tube V12 to conduct. Relay 22 is energized and applies platecurrent 3+ to preamplifier tube V8A through contacts 22A, 22C. Contacts22A, 22B open and deenergize the plate circuit of preamplifier tube V7B.Thus, the new frequency established by reed oscillator 11C is used tocontrol the output of amplifier tube V10 and is available at outputterminal OT.

Further increases in trafiic density and the potential applied to line42 will result in further stepping of the level detector. When trafficdensity approaches its highest value, level detector tube V15 willconduct and energize relay 25. Contacts 25A, 25C will close and supplyplate potential B+ to tube V9B making preamplifier V9B and reedoscillator 11F effective. In the application of the level detector totraffic cycle length control the lowest level oscillator will generatethe highest frequency which in turn drives the cycle timing motor at thehighest speed resulting in a short cycle length. The highest leveloscillator will generate the lowest frequency resulting in a long cyclelength.

To complete the description, assume now that traffic density decreasesand that the potential from the voltage detector VD applied to the leveldetector grids also decreases. If level detector tube V12 has beenconducting, for example, and now its bias potential is no longersufiicient to sustain conduction, the tube will cease to conduct whenthe A.C. potential from line L2 goes through its negative half-cycle.Plate circuit relay 22 will be deenergized closing contacts 22D, 22Eadmitting L2 power to the plate of the next lower level detector tubeV11. The potential from the voltage detector VD will be sufficient topermit tube V11 to conduct because traffic density cannot fall offinstantaneously. When relay 22 was deenergized it removed platepotential from preamplifier tube VSA; when relay 21 was energized itapplied plate potential to preamplifier tube V7B. Thus, the frequencydeveloped by reed oscillator 11B replaces that developed by reedoscillator 11C.

Thus the appropriate traffic cycle control frequency is selected fromamong a group of continuously generated frequencies and made availableat an output terminal for control of a number of local traffic signalcycle controllers. The output frequency is inversely proportional totraffic density level and results in a trafiic signal cycle whoseduration is proportional to traffic density.

Because the output of the device is a frequency variable signal it lendsitself to the common methods of transmission. Examples of methods oftransmission are:

(a) Single conductor, and common return.

(b) Telephone pair.

(0) Radio.

Each of these systems will be explained further and then the local cycleselector apparatus will be described.

Transmission Systems Various known methods are available fortransmitting the variable frequency signal from the cycle generator andselector in the master controller to the cycle timing devices in thelocal trafiic controllers. These may include one conductor plus a commonreturn in the control cable, a leased telephone pair, or a radio link.

Normally a multi-conductor cable connects the master controller with agroup of local intersection trafiic controllers. One conductor in thecable may be reserved for the cycle length control function and may haveimpressed on it the variable frequency signal. At each local controllerthe variable frequency is applied as a signal to an amplifier. Theamplifier has a very high input impedance to limit the drain on theline. It may also incorporate the novel feature of providing an outputfrequency identical to its input frequency at a potential proportionalto 1 1 frequency. The output potential is increased with frequency tocompensate for higher iron and copper losses within the synchronousmotor operating at frequencies up to twice or more its design frequency.

In the event a multi-conductor cable is not employed between the mastercontroller and the local controllers, or in the event a multi-conductorcable is employed but all of the conductors are being used for otherfunctions, a pair of telephone wires may be leased from the localtelephone company. Various transmission plans may be investigated andpriced. Assuming that the leased pair has been found to be mosteconomical in this instance, the variable frequency signal would beapplied to the telephone pair through an impedance matching device.Reduction in signal strength at distant controllers is not a detrimentbecause the amplifiers in the local controllers depend on inputfrequency rather than voltage. Thus the variable frequency system issuitable for interconnection by wire.

A radio link is likewise a suitable interconnecting means. A frequencymodulated transmitter may be installed at a central station and an FMreceiver installed at each local controller. This system is shown inblock diagram in FIGURE 5 and is described below. It is more fullydisclosed in United States patent application 830,096, named above.

Referring now to FIGURE 5, the potential from the higher traffic densitycomputer IC or OC arrives via the voltage detector VD and is applied asthe input signal to the cycle generator and selector units CS. Asdescribed in a prior section, the various cycle generators oscillatecontinuously, a level detector selects one oscillator and amplifiers itsoutput, and makes it available at output terminal OT. The outputconsists of one of a group of fixed frequency signals of from 30 to 120c.p.s. depending on trafiic density. The signal frequency is applied tothe tone sensitive modulator TSM. A constant frequency tone generator TGdevelops a tone at a constant frequency, say 3,000 cycles per second.The 3,000 c.p.s. constant frequency is amplitude modulated by one of the30 to 120 c.p.s. frequencies from the cycle generator and selector inthe modulator TSM. This signal is amplified and applied to a frequencymodulated radio transmitter TR for broadcast to the local controllers.

The cycle selector unit CS is normally located in the master controllerand its output is fed to the modulator TSM and transmitter TR which maybe installed at a location near the antenna.

At each local controller an antenna and an F M receiver XR picks up thesignal, amplifies it, detects the modulated 3,000 c.p.s. carrier, andapplies it to a twin T network TT having inverse feedback. The twin Tnetwork blocks out substantially all but the 3,000 c.p.s. signal,amplifies it, and passes it to a tone sensitive demodulator TSD whichmay be a standard detector. The detector rectifies the signal and passesit through a low pass filter to permit only the 30 to 120 c.p.s. portionto pass to amplifier A. The 30 to 120 c.p.s. variable frequency is thenamplified and applied to the cycle timing motor M. The speed of motor Mfixes the duration of the cycle change at the local controller. Sinceeach controller motor M is synchronous and is energized by a commonfrequency the cycle duration at each controller is identical with veryother controller including the master. This is a desirable feature andhas not been possible in the past except when all the timing motors weredriven from 60 c.p.s. local power.

The Local Controller One form of local traffic cycle controlling deviceis shown in isometric view in FIGURE 6. Dial 202 determines the durationof one complete cycle of trafiic signal change and is driven throughsuitable gearing (not here shown) by synchronous motor 60 energized overline VF from the variable frequency power source. The variable frequencypower source is the output terminal OT of 12 the cycle generator andselector CS, FIGURE 4, connected to line VF over one conductor of aninterconnecting cable CC or over a radio link as shown in FIG- URE 5.Dial 202 runs continuously at a constant speed for each input frequency.

Dial 202 carries five keys 100, 101, 101, 102, 103 angularly displacedon its surface. Key 100, normally inserted in the zero slotcorresponding to the zero point in a traffic signal cycle, closescontacts 1008 as it passes beneath them and momentarily energizesconstant speed motor 37. Motor 37 drives constant timing dial 203through suitable gearing (not here shown) and rotates it sufficiently topermit key 32 to move from under contacts 32S allowing them to close andenergize motor 37 for half a revolution of dial 203.

Constant timing dial 203 times the duration of all intervals in thesignal cycle which are not allowed to vary with changing cycle duration.Examples of signals whose duration is constant include amber trafiicclearing intervals, guaranteed pedestrian clearance intervals, advancegreen arrow intervals, all red clearing intervals, no left turnintervals, and similar intervals. The duration of each of the aboveintervals is determined by the placement of dial keys 74, 74', 78, S0,30', and 31, and by the number of intervals broken out of itssignal-controlling cam. Contact 305 is closed momentarily by keys 74,74-, 73, S0, to energize solenoid 48 and thereby ratchet camshaft 4-6one position. If a signal is controlled by a cam similar to cam 59broken out for more than one interval, the signal will be illuminatedfor more than one interval. If a signal is controlled by a cam similarto cam 44 broken out for only one interval it will be illuminated foronly that interval. The intervals may be given any reasonable durationby the relative spacing of the dial keys on dial 203 and by the speedor" dial 203 governed by synchronous motor 37 and gearing. The presentform of the invention permits easy change of gears between motor 37 anddial 203 to permit longer or shorter constant timing intervals. Once thegear is installed. there is little need for change.

To illustrate a typical signal cycle assume that the green signal isilluminated to cross street trafiic and the walk signal is illuminatedto permit pedestrians to cross the main street. As illustrated in FIGURE6 key on dial 202 has just closed contact 1008 momentarily energizingmotor 37 through line 57 and switch 708. Motor 37 starts to turn dial203 and the movement of key 32 from under contacts 328 permits them toclose and energize motor 37 from a steady source L2. Dial 203 begins torotate, timing the end of the cross street green interval. Rotation ofdial 203 brings key 74' under contacts 308 closing them momentarily toenergize solenoid 48 and ratchet camshaft 46 one position. Thepedestrian walk signal 2W is deenergized by the action of cam 44' andswitch 448'. The pedestrian Wait signal 2WT is illuminated by the actionof cam 43' and switch 438'.

A guaranteed pedestrian clearance interval is timed by the spacingbetween the keys 74 and 78. The duration of the interval desired dependsupon the width of the intersection and is intended to permit safepassage for a person starting to walk across main street at the end ofthe walk interval. The wait signal 2WT is illuminated when thesafe-passage time has expired prior to the award of righ-of-way to mainstreet traffic.

Dial 203 continues to revolve bringing key 78 under contacts 308 whichcloses them and momentarily energizes solenoid 48 which turns camshaft46 one position. Cam 44 controlling the cross street green signal 2Gopens its switch 448 deenergizing the signal 2G. Cam 43 closes itsswitch 438 energizing the cross street amber signal 2A. Dial 203 timesthe duration of the amber interval. Closure of contacts 308 by dial key80 terminates the amber interval and starts the main street greeninterval and the main street pedestrian interval.

Cam 43 opens switch 438 deenergizing the cross street amber signal 2A.Cam 41 closes switch 418 illuminating the main street green signal 16.Cam 41' closes switch 41S illuminating the walk signal 1W parallel tomain street. Switch 435 continues to illuminate the wait signal 2WTacross main street. Cam 45 closes switch 458 illuminating the crossstreet red sign-a1 2R. Cam 49 opens switch 498 deenergizing coil 70,closing switch 708 to line 58, transferring control of motor 37 fromcontacts 325 to contacts 338. Dial 203 rotates a few degrees and stopswhen key 33 opens contacts 338 deenergizing motor 37.. Dial 202 rotatescontinuously timing the main street green interval and the 'walkinterval parallel to main street.

The duration of these right-of-way intervals is timed by variable timingdial 202. The beginning of the end of the walk interval is initiatedwhen one of the split keys 101, 101, 102, or 103 closes itscorresponding contact 101$, 101$, 1028 or 1038 and momentarily energizesmotor 37 over conductor 58 and switch 708. Which of the split keys iseffective is determined by the position of contacts 108, 118, and 118.The latter contacts are controlled by relays and 11 from a mastertraflic controller, not shown. The functioning of the split control isdescribed fully in United States patent application 742,160, filed June16, 1958, entitled Trafiic Cycle Split Selectors.

Relay 70 is deenergized and switch 70S is closed to conductor 58 duringthe main street green interval because its controlling cam 49 is not cutfor that interval.

Therefore, when key 103 closes contact 1038, for example, power issupplied to motor 37 to start it rotating dial 203. As SOOn as key 33moves out from under contacts 338 the latter close and supply steady L2power to motor 37. Motor 37 is thus energized for half a revolution ofdial 203 until contacts 328 are opened by key 32. Dial 203 rotates onlya short distance until it brings key 80 under contacts 308 closing themmomentarily and ratcheting camshaft 46 into a new position. Cam 41'opens switch 418 deenergizing the walk signal 1W parallel to mainstreet. Cam 40 closes switch 408 energizing the wait signal 'lWTparallel to main street.

Dial 203 rotates at a constant speed and times the guaranteed pedestrianclearance interval. When key 31 reaches and momentarily closes contacts318 the solenoid 48 is again energized and ratchets the camshaft 46' toits next position. Cam 40 closes switch 408 illuminating the main streetamber signal 1A. Cam 41 opens switch 418 deenergizing the main streetgreen signal 1G. Dial 203 times the constant amber interval whichterminates when key 74 closes contacts 305 and ratchets the camshaft toits next position. Cam 40 opens switch 408 deenergizing the main streetamber signal 1A. Cams 42 and 44 close switches 42S and 445,respectively, illuminating the main street red signal IR and the crossstreet green signal 26. Cam 44' closes switch 448 illuminating the walksignal 2W across main street. Cam 43 opens switch 438 deenergizing thewait signal 2WT across main street. Thus the cross street right-of-Wayinterval is in progress, its variable portions timed by dial 202 and itsfixed portions by dial 203. If it had other variable intervals such asleft or right turn arrow indications, they would be timed by thevariable timing dial 202. If it had other fixed time intervals such asall red clearance, they would be timed by consant timing dial 203.

It is to be noted that a circuit is employed to keep the variable timingdial 202 in step with the proper phase of the camshaft 46. Key 100 timesthe beginning of the end of the cross street interval and camshaft 46must be in the cross street interval to make contacts 1008 effectivethrough switch 705. Switch 7 08 is closed to line 57 only when relay 70is energized. Relay 70 is energized only during the cross street greeninterval through switch 498 operated by cam 49. Thus, key 100 always 14times the beginning of the end of the cross street green interval, whichis the same as the start of the main street green interval, and thesplits always occur in the proper part of the cycle.

Another circuit is provided to keep the constant timing dial 203 in stepwith camshaft 46. Contacts 308 are ineffective to ratchet the camshaftduring the main street green interval. Only key 31 and contacts 318 areeffective to release the camshaft from the main street green interval.Switch 598 controlled by cam 59 is open during that interval, renderingcontacts 308 ineffective. Thus, the camshaft 46 is kept in step with theproper interval on the variable timing dial 203 so that the intervals onthe dials 202, 203 correspond with the intervals on the camshaft 46.

The circuit employed to keep dial 202 in synchronism with the mastercontroller is not shown. It is fully described in United States patentapplication 768,193, filed October 20, 1958, entitled Trafiic CycleOffset Selector, and in application 642,469, filed February 26, 1957,entitled Multiple Program Traffic Control Systems. It will beappreciated that a reference cam (not shown) in each local controllermay be driven also by motor 60 at the same speed as dial 202 and asimilar cam located in the master controller driven also from the samevariable frequency source OT. The resynchronizing circuit maintains azero angular relationship between the reference cam in the mastercontroller and the reference cam in each local controller, thus keepingall controllers in exact synchronism. An offset establishing device, notshown here but described in application 768,193 named above, inserts aremotely selectable angular displacement between dial 202 and the localreference cam. Any local controller may be made to lead or lag anyneighboring controller by a remotely selectable angle, and thus by partof a trafiic signal cycle. This establishes a progression for trafficmoving along a thoroughfare or in a grid.

In the above discussion of the relationship between the variableportions of the traffic signal cycle, the right-ofway portion for eachdirection of traffic is understood to include also the fixed amberinterval. The right-of-way periods are thus proportional to cyclelength; the intervals during which the green signals are illuminated arenot exactly proportional to cycle length because of the fixed a-mberintervals.

I claim:

1. A method of adjusting traffic cycle length on a street in relation tothe density of traffic in the heavier direction thereon, comprising,counting traffic in each direction and developing an output potentialproportional thereto, comparing the two potentials and utilizing onlythe higher, admitting the higher potential to a level detector having asuccession of levels, energizing a level of one of said succession oflevels corresponding to the level of the potential, operating aplurality of signal generators continuously to produce a plurality ofoutput signals of different frequencies, the energized level of saidlevel detector applying the output signal of one of the signalgenerators to an amplifier, transmitting the amplified output to aseries of local traffic controllers, energizing a synchronous motor ineach controller from the amplified output, driving a traffic cycletiming dial by the motor, the duration of a traffic cycle beingproportional to the heavier traffic count.

2. A traific cycle length selector and frequency generator including, incombination, a plurality of successively higher biased voltage leveldetectors having a common input connection, a plurality of relays onefor each said level detector and each of said relays adapted to beselectively energized by its corresponding level detector, a pluralityof continuously oscillating tone generators one for each said leveldetector and each of said tone generators adapted to produce a tonehaving a frequency different from that produced by the other saidgenerators, a source of potential, each of said relays when energizedconnecting said potential to a tone generator corresponding to theenergized relay and disconnecting said source of potential 15 from anyother tone generator, an amplifier, the output of all tone generatorsadapted to be connected to said amplifier with only the output from thetone generator corresponding to the energized relay being amplified.

3. A traffic cycle length selector as in claim 2 including aninterconnecting channel to which the output of said amplifier isapplied, a plurality of local tratfic signal controllers, a synchronousmotor in each said local controller connected to said interconnectingchannel and adapted to be energized therefrom.

4. A traffic cycle length selector as in claim 3 including a timing dialin each controller adapted to be driven by said motor, a multi-circuitsignal controller intermittently stepped by said timing dial, a sourceof power, and a plurality of traffic signals connected to said source ofpower through said multi-circuit controller in a traffic controllingpattern, the duration of said pattern controlled by the speed of saidmotor and said tone generator.

5. A local traffic signal control device including a first synchronousmotor, a first dial drum adapted to be driven by said motor, a source ofinput potential for energizing said synchronous motor, said inputpotential having a variable frequency constant for a time period usuallylonger than a trafiic signal cycle, a plurality of contact pairsadjacent to the surface of said first dial drum, a plurality of keysarranged in angular relationship on said first dial drum and adapted toclose particular ones of said contact pairs, a second motor, a seconddial drum adapted to be driven by said second motor, a first and secondplurality of contact pairs adjacent to the surface of said second dialdrum, a plurality of keys arranged in angular relationship on saidsecond dial drum in operative relationship with said first and secondcontact pairs, a source of power, a circuit comprised of said source ofpower and said first plurality of contacts adjacent to said second dialdrum and said plurality of contacts adjacent to said first dial drum tointermittently momentarily energize said second motor and then tomaintain energized said second motor for portions of a revolution ofsaid second dial, a solenoid op erated camshaft intermittently energizedby said second plurality of contact pairs adjacent to said second dialdrum, a traffic signal cycle having constant and trafiic-variableintervals, the duration of said constant intervals fixed by said seconddial, and the duration of said traflic variable intervals fixed by saidfirst dial and said variable frequency.

6. A local traffic signal controller including a variable speed dialdriven by a motor energized by variable frequency power from a remotesource, a constant speed dial driven by a motor energized by constantfrequency power from a local source, adjustable contacts in operativerelationship with said variable speed dial that place the constant speeddial motor in operation at intervals, a step switch, adjustable contactsin operative relationship with said constant speed dial that close acircuit to intermittently energize said step switch, said step switchstepped at intervals alternately timed by said variable speed dial andsaid constant speed dial, and traffic signals controlled by said stepswitch.

7. In a trafiic regulated trafiic control system, a plurality of localtrafiic signal cycle controllersleaeh including first and second timingmeans connected respectively to fixed and variable frequency channels totime constant and variable portions of the traffic cycle respectively, amaster controller connected to said plurality of local controllers, saidsecond timing means employed also in said master controller andenergized constantly from said variable frequency channel forsynchronizing said second timing means in each said local controllerwith said second timing means in said master controller.

8. A cycle generator comprising a plurality of constant frequencygenerators each functioning continuously and each developing asuccessively lower frequency, a like plurality of preamplifiers eachconnected to and adapted to receive signals from each said frequencygenerators, but only one of said preamplifiers effective at any one timeto transmit a frequency received by said frequency generators, a likeplurality of voltage sensing devices each having a manuallypreselectable successively higher bias and adapted to detectsuccessively higher input voltages and having circuit interrupter meansconnected to cut off all of said voltage sensing devices but that whichis energized having the highest bias, said voltage sensing devices andhaving circuit switching means connected to energize its correspondingpreamplifier; an input circuit common to all of said volt-age sensingdevices; an amplifier having an input circuit connected at all times toall of said preamplifiers and amplifying only the output of theenergized preamplifier; and an output circuit from said amplifier.

9. A cycle generator as in claim 8, each said constant frequencygenerator comprised of a reed vibrator and a vibrating reed signalgenerator and an electronic oscillation initiating and sustainingcircuit to start said reed vibrating and to amplify the signal output ofthe vibrating reed signal generator and to feed said amplified signalback to said reed vibrator to develop and maintain oscillation, and anoutput circuit between each said generator and each said preamplifier.

10. A cycle generator as in claim 8, each said voltage sensing devicecomprising of a tetrode gas-filled tube having a cathode, a plate, acontrol grid, and a screen grid; the cathode and screen grid of eachsaid tube connected together and to ground, the control grid of eachsaid tube connected through an impedance to said common input circuitand to a manually adjustable tap on a voltage dividing network; a sourceof negative bias potential, a like plurality of voltage dividingnetworks connected between said negative potential and ground, each saidtap normally set for a successively more negative bias potential; asource of alternating current potential, a plurality of relays each onein circuit with the plate of each said tube and with said AC, potentialthrough a first ladder circuit, said first ladder circuit comprised of apair of contacts on each of said relays and a series circuittherebetween; a source of plate potential, a second ladder circuitcomprised of a second set of contacts on each of said relays in circuitwith said plate potential and with the plate circuit of each saidpreamplifier such that only the one voltage sensing device correspondingto the value of input voltage is operative at a time to make itscorresponding preamplifier effective.

11. A trafiic cycle length generator and selector including an inputcircuit and an output circuit; a source of plate potential and a sourceof bias potential; a plurality of tetrode gas-filled tubes, each havingat least a cathode, plate, and grid; each of said grids connectedthrough an impedance to said input circuit; each of said cathodesconnected to ground; a like plurality of stepped, manually adjustablepotential dividers connected in common between said source of biaspotential and ground, each of said potential dividers having a manuallyadjustable tap connected to and biasing each of said grids the biasapplied to each of said control grids increasing from the bias appliedto the control grid of one of said tetrode tubes to the bias applied tothe control grid of the next succeeding tetrode tube within saidplurality of tetrode tubes; a like plurality of relays having contacts,one of said relays in the plate circuit of each of said tetrode tubes,each plate circuit including contacts on all preceeding relays inhigher-biased tube circuits; each relay also having contacts which applythe plate circuit potential to the plate of its correspondingpreamplifier tube, a plurality of corresponding preamplifier tubes eachhaving a cathode, plate and grid; each of said cathodes connected toground through an impedance; an amplifier tube having at least acathode, plate and grid, said amplifier tube grid connected to groundthrough an impedance and to the plate of each of said preamplifier tubesthrough an impedance, said amplifier tube plate connected to said sourceof plate potential, said amplifier tube cathode connected to groundthrough an impedance forming a cathode follower, said output circuitconnected also to said cathode through an impedance; a like plurality ofoscillator control circuits each comprised of a reed oscillator and adouble triode vacuum tube; each said reed oscillator having a primaryand secondary excitation coil and two tuned reeds mechanically joined;each of said double triode vacuum tubes having first and secondcathodes, first and second plates, and first and second grids; eachprimary excitation coil in circuit with said second cathode and ground,each secondary excitation coil connected between said first grid andground, said first cathode connected through an impedance to ground,said first and second plates connected through impedance to said sourceof plate potential, said second grid connected through impedances toboth said first plate and to ground, said second plate connected throughimpedance also to ground, and said first plate connected throughimpedance to the grid of its corresponding preamplifier tube, saidimpedances in said oscillator control circuit selected to initiate andsustain oscillation.

12. A method of determining trafiic cycle length on a thoroughfare inrelation to the density of traffic moving in the heavier directionthereon, the steps of which com prises, counting traffic moving in eachdirection over a running interval and developing a potentialproportional thereto, comprising the two potentials representative oftrafiic density and selecting the higher, applying the higher potentialto a multi-level voltage level detector and allowing the potential toenergize one level of said multi-level detector depending upon the valueof the potential, operating a plurality of tone generators continuouslyto produce a corresponding plurality of different output tone signals,amplifying the output tone signal of one of said tone generatorscorresponding to the energized level of said multi-level detector,transmitting the amplified tone signal to a group of local trafficsignal controllers, operating a synchronous motor at each localcontroller from the transmitted amplified tone, and driving a cycletiming dial from the synchronous motor, the frequency of the transmittedamplified tone determining the speed of the motor and the timing of thetraffic cycle.

13. A traffic control system comprising: inbound and outbound trafiicdensity computers each delivering a voltage indicative of the traflicdensity; a voltage detector adapted to receive and pass the higher ofsaid voltages; a number of successive level detectors, connected toreceive the transmitted voltage of said voltage detector, each saiddetector responsive to a higher voltage than the preceding leveldetector; a like number of relays each one actuated by a level detectorwith which it is associated, and when energized to deenergize all leveldetectors responsive to a lower value of said voltage; a plurality oftone generators each of which is associated with one of said leveldetectors, such that a tone generator transmits a tone signal when thelevel detector with which it is associated is energized; a conductorover which said tone signal is transmitted; a plurality of localcontrollers to which said conductor leads; a synchronous motor in eachlocal controller connected to said conductor and driven at a speeddetermined by said transmitted tone; and a trafiic cycle timingmechanism driven by said synchronous motor.

14. A trafiic control system, comprising: an inbound and outboundtraffic density computer, said computer having an output voltageproportional to traffic density; a voltage detector to determine andtransmit the higher of the two said outputs; a succession of leveldetectors to which said higher voltage is applied for selectivelyenergizing one of said level detectors; a plurality of re lays, each oneof said relays corresponding to and associated with one of said leveldetectors and connected thereto, such that each one of said relays isenergized when its corresponding level detector is energized and iseffective to deenergize all other lower level detectors; a succession ofcontinuously operating tone generators corresponding to said relays,each of said tone generators adapted to produce a tone having afrequency different from that produced by any other tone generator insaid succession; an amplifier; said relay corresponding to the energizedlevel detector also switching the output of its corresponding tonegenerator to said amplifier; a plurality of local intersection trafficsignal controllers; a conductor interconnecting said amplifier with eachsaid controller, the output of said amplifier applied to said conductor;a synchronous motor in each of said local controllers, said motorconnected to said conductor and adapted to be operated therefrom at aspeed proportional to the said tones; and trafiic cycle timing means ineach said controller driven by said motor.

15. A traffic cycle length selector and generator, including, incombination: a source of input potential representative of traflicvolume in the heavier direction of tralfic fiow on a thoroughfare; aplurality of adjustable level detectors set for successively highervalues of said input potential, each of said level detectors responsiveto different Values of said input potential; a plurality of fixedfrequency generators, each of said generators adapted to develop andtransmit a dfierent frequency; circuit means connecting the first ofsaid frequency generators to said level detectors wherby the first ofsaid frequency generators transmits its frequency when none of saidlevel detectors is energized, a second of said frequency generatorseffective to transmit its frequency when the first of said leveldetectors is energized, the third of said frequency generators effectiveto transmit its frequency when the second of said level detectors isenergized; an amplifier connected to receive the transmitted signalfrequency of whichever frequency generator is transmitting, saidamplifier having an output frequency substantially identical with itsinput frequency.

16. A local trafiic signal control device, including, in combination: afirst synchronous motor; a first dial drum adapted to be driven by saidfirst motor; a source of input potential for energizing said firstmotor, said input potential having a variable frequency constant for aperiod normally longer than a traffic signal cycle; a plurality of firstcontact pairs adjacent to the peripheral surface of said first dialdrum; a plurality of keys angularly spaced about the periphery of saidfirst dial drum and adapted to close particular ones of said contactpairs; at second motor; a second dial drum adapted to be driven by saidsecond motor; a first plurality of keys arranged in spaced angularrelationship about the periphery of said second dial drum; a firstplurality of contact pairs adjacent to the peripheral surface of saidsecond dial drum; a source of power; a circuit comprising said source ofpower and said contact pairs adjacent to said first dial drum and saidfirst plurality of contacts adjacent to said second dial drum, saidcircuit adapted to intermittently energize said second motor, said firstplurality of contact pairs adjacent to said second dial drum adaptedalso to intermittently maintain energized said second motor; a stepswitch device; a second plurality of keys on said second dial drum; asecond plurality of contact pairs adjacent to said second dial drum,adapted when closed by said selected ones of said second plurality ofkeys to momentarily energize said step switch device; a plurality ofsignals and signal circuits controlled by said step switch through acycle of traffic signal change having fixed and variable intervals, theduration of the variable intervals dependent on the speed of said firstmotor and said variable frequency potential, and the duration of theconstant intervals dependent on the speed of said second motor.

17. A trafiic cycle length generator and selector including, an inputcircuit and an output circuit; a source of plate potential and a sourceof bias potential; a plurality of tetrode gas-filled tubes, each havingat least a cathode, a plate, a control grid, and a screen grid, each ofsaid control grids connected through an adjustable of said controlgrids, the bias applied to each of said con:

trol grids increasing stepwise from the bias applied to the control gridof one of said tetrode tubes to the bias applied to the control grid ofthe next succeeding tetrode tube within said plurality of tetrode tubes;a like plurality of relays having contacts, one of said plurality ofrelays in a plate circuit of each of said tetrode tubes; each said platecircuit of said tetrode tubes also including contacts on all said relaysin the plate circuits of tubes having control-grids of higher-bias; aplurality of preamplifier tubes corresponding to said relays, eachhaving a cathode, a plate, and a grid; each relay also having contactswhich apply the plate. circuit potential to the plate of itscorresponding preamplifier tube; the cathodes of said preamplifier tubesconnected to ground through an impedance; an amplifier tube having atleast a cathode, a plate and a grid, said amplifier tube grid connectedto ground through an impedance and to the plate of each of saidpreamplifier tubes through an impedance, saidamplifier tube plateconnected to said source of plate potential, said amplifier tube cathodeconnected to ground through an impedance forming a cathode follower,said output circuit connected also to said cathode through an impedance;a like plurality of oscillator control circuits, each comprised of areed oscillator and a double triode vacuum tube, each said reedoscillator having a primary and a secondary excitation coil and tWotuned reeds mechanically joined; each of said double triode vacuum tubeshaving first and second cathodes, first and second plates,

n I and first and second grids; each primary excitation coil in circuitwith said second cathode and ground, each sec-.

ondary excitation coil connected between said first grid and ground,said first cathode connected through an impedance to ground, said firstand second plates connected through an impedance to said source of platepo tential, said second grid connected through impedances to both saidfirst plate and to ground, said second plate connected throughimpedances also to ground, and said first plate connected throughimpedance to the grid of its corresponding preamplifier tube, saidimpedances in said oscillator control circuits chosen to initiate andsustain oscillation.

References Cited in the file of this patent UNITED STATES PATENTS1,945,666 Stewart Feb. 6, 1934 1,973,563 Friendly Sept. 11, 19342,199,573 Paul May 7, 1940 2,282,102 Tunick May 5, 1942 2,282,142 BarkerMay 5, 1942 2,291,855 Wilcox Aug. 4, 1942, 2,301,004 Adler Nov. 3, 19422,428,389 Singer Oct. 7, 1947 2,515,254 Nosker July 18, 1950 2,538,829Clark Jan. 23, 1951 2,542,978 Barker Feb. 27, 1951 2,554,329 Hammond May22, 1951 2,564,766 Oberman Aug. 21, 1951 2,612,550 Jacobi Sept. 30, 19522,761,119 Barker Aug. 28, 1956 2,761,120 Wilcox Aug. 28, 1956 2,892,995Kearney June 30, 1959 UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent No. 3,047,838 July 31, 1962 George Donald Hendricks Itis hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 17, line 26 for "comprising" read comparing Signed and sealedthis 5th day of November 1963.

(SEAL) Attest:

EDWIN L. REYNOLDS ERNEST W. SWIDER Attesting Officer AC g Commissionerof Patents

